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Date: Sat, 18 Feb 2023 13:56:38 +0100
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To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
From: Tomas Vondra <tomas.vondra@enterprisedb.com>
Subject: occasional valgrind reports for handle_sig_alarm on 32-bit ARM
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Hi,

I've been running a lot of valgrind tests on 32-bit arm recently, and
from time to time I get a failure in handle_sig_alarm like this:

    ==13605== Use of uninitialised value of size 4
    ==13605==    at 0x88DA98: handle_sig_alarm (timeout.c:457)
    ==13605==    by 0xFFFFFFFF: ???
    ==13605==  Uninitialised value was created by a heap allocation
    ==13605==    at 0x8A0374: MemoryContextAllocExtended (mcxt.c:1149)
    ==13605==    by 0x86A187: DynaHashAlloc (dynahash.c:292)
    ==13605==    by 0x86CB07: element_alloc (dynahash.c:1715)
    ==13605==    by 0x86A9E7: hash_create (dynahash.c:611)
    ==13605==    by 0x8A1CE3: EnablePortalManager (portalmem.c:122)
    ==13605==    by 0x8716CF: InitPostgres (postinit.c:806)
    ==13605==    by 0x653F63: PostgresMain (postgres.c:4141)
    ==13605==    by 0x5651CB: BackendRun (postmaster.c:4461)
    ==13605==    by 0x564A43: BackendStartup (postmaster.c:4189)
    ==13605==    by 0x560663: ServerLoop (postmaster.c:1779)
    ==13605==    by 0x55FE27: PostmasterMain (postmaster.c:1463)
    ==13605==    by 0x4107F3: main (main.c:200)
    ==13605==
    {
       <insert_a_suppression_name_here>
       Memcheck:Value4
       fun:handle_sig_alarm
       obj:*
    }

or (somewhat weird)

    ==23734== Use of uninitialised value of size 4
    ==23734==    at 0x88DDC8: handle_sig_alarm (timeout.c:457)
    ==23734==    by 0xFFFFFFFF: ???
    ==23734==  Uninitialised value was created by a stack allocation
    ==23734==    at 0x64CE2C: EndCommand (dest.c:167)
    ==23734==
    {
       <insert_a_suppression_name_here>
       Memcheck:Value4
       fun:handle_sig_alarm
       obj:*
    }

It might be a valgrind issue and/or false positive, but I don't think
I've seen such failures before, so I'm wondering if this might be due to
some recent changes?

It's pretty rare, as it depends on the timing of the signal being just
"right" (I wonder if there's a way to increase the frequency).


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company